Addison’s Disease in Dogs

Addison’s disease or hypoadrenocorticism is the result of decreased hormone production in the cortex (outer part) of a dog’s adrenal glands.

Located close to the kidneys, the adrenal glands are a pair of small glands, each comprising an outer cortex and an inner medulla.  These glands produce two vital hormones: cortisol, a stress hormone, and aldosterone, a hormone that regulates the body’s levels of sodium and potassium.  The proper level of these two minerals is essential for maintaining the body’s fluid balance.

While the disease is primarily the result of an immune–mediated destruction of adrenal tissue, it’s caused less often by infection, cancer or trauma having damaged the adrenal glands.  It may also occur after a dog’s been treated for Cushing’s disease (hyperadrenocorticism) when too much cortisol and aldosterone are produced.  Should that medication inadvertently suppress too much adrenal gland activity or damage the gland, the result may be a deficiency of cortisol and aldosterone.

A secondary form of Addison’s disease can be caused by a defect or a tumor in the pituitary gland which is an important hormonal regulator in the brain.  It can also develop if a dog has been treated with long-term steroids that have suddenly been stopped. Known as iatrogenic hypoadrenocorticism, the condition is usually temporary.

Clinical signs of this disease are usually vague and can include lethargy, diarrhea, vomiting, increased thirst, increased urination, unplanned weight loss, and intermittent shaking episodes that may wax and wane.  While such non-specific treatments as the administration of fluids or the use of corticosteroids may help temporarily, the signs will soon return. And if they do, Addison’s disease may be the culprit.

Sometimes, however, a dog’s symptoms may appear abruptly and severely, causing an Addisonian crisis. These symptoms include sudden weakness, severe vomiting, diarrhea, and sometimes collapse. Deemed a true medical emergency, prompt hospitalization, and supportive treatment are a must.

Any diagnosis is based on a dog’s medical history, including his medications, clinical signs, and the results of blood and urine tests – with special attention being paid to electrolyte imbalances.  The most definitive diagnostic test for Addison’s disease, however, is the ACTH-stimulation test where his cortisol levels are measured before and after an injection of a synthetic form of ACTH (adrenocorticotropic hormone).  To rule out a different cause, additional tests such as basal cortisol levels, natural plasma ACTH, an ECG, x-rays, and an abdominal ultrasound may be performed. In rare instances, a CT or MRI may be needed to diagnose a pituitary gland problem.

Fortunately, though, most dogs with Addison’s disease can be successfully treated once diagnosed. This typically involves the use of Desoxycorticosterone pivalate or DOCP (brand names Percorten®-V or Zycortal®), an FDA-approved medication injected every three to four weeks, depending on the dog, which replaces the missing mineralocorticoid aldosterone. After a brief training lesson, DOCP injections can be administered at home instead of at the vet’s office, and they’re often supplemented with an oral glucocorticoid.

While DOCP may not be suitable for every dog, some do their best on oral medications that replace both the mineralocorticoid and the glucocorticoid such as fludrocortisone (brand name Florinef®). An affected dog’s diet and activity levels can often remain the same, and most dogs can continue to lead normal and loving lives.